The invention relates to a method for generating a jet of dry ice particles, wherein liquid carbon dioxide is expanded in an expansion space in order to form the dry ice particles which are then introduced into a flow of a carrier gas, and to a device for carrying out this method.
Such a method and device have been disclosed in WO 2004/033154 A1. The device forms part of a blasting equipment which serves to remove firmly adhering incrustations from larger surfaces such as the internal surfaces of pipes or boilers in industrial plants. The liquid carbon dioxide is introduced from a supply line that is formed by a capillary, for example, into an expansion space having a larger cross-section, so that, by expansion, a portion of the carbon dioxide is evaporated while another portion of the carbon dioxide condenses to dry ice particles due to the evaporation chill. The expansion space opens, preferably laterally, into a blasting line through which a carrier gas such as compressed air or nitrogen is passed. Thanks to the drag of the carrier gas flowing past the mouth of the expansion space, the dry ice particles are, so to say, sucked out of the expansion space and are suspended in the flow of carrier gas. A nozzle, preferably a Laval nozzle, is provided at the end of the blasting line, so that the jet is accelerated to high speeds, preferably supersonic speeds.
In one embodiment described in this document, the expansion space is formed by a pipe section that has an internal thread. This internal thread is supposed to form disturbance edges at which a crust of dry ice shall be formed by the impinging dry ice particles. This is based on the theory that larger dry ice particles would be formed by crumbling of the crust. As an alternative to the internal thread, disturbance edges are mentioned, that are formed by inserts such as an impeller wheel or a worm in the interior of the expansion space. In this context, it has heretofore been assumed that the disturbance edges shall serve as targets for the dry ice to impinge on, but, on the other hand, shall not hamper the discharge of the dry ice particles and the gas from the expansion space, because, otherwise, the pressure in the expansion space would become too large and hence the expansion and evaporation of the liquid carbon dioxide would be compromised.